We’re on the Cusp of the 6th Mass Extinction Event. Can We Halt it in Time?

The Earth may already have begun its descent into its sixth “mass extinction” event. Where the previous five were caused by external influences like meteor strikes or huge volcanic eruptions, this one is different.

This time, say scientists, the finger of blame points undeniably at us.

A collection of studies published this month in Science Magazine review the evidence that points to this sobering finding. If we don’t change our ways, they say, the Earth may well see the end of the Anthropecene period – the Age of Humans.

A mass extinction event means a rapid, widespread loss of life on Earth. From an evolutionary perspective, it means more species go extinct than new ones that flourish. Depending on the cause, between 70 to 90 percent of all species just disappear.

Taking all previous mass extinctions into account, scientists say that nine out of 10 of all types of life ever to have lived on this planet have gone extinct.

Mass extinction occurs due to a distinctive domino effect that’s triggered by “defaunation.” To regular Joes like you and me, this means a decline in animal population. Scientists believe we’re entering a period of “Anthropocene defaunation” – loss of animal population caused by human activity.

How do we cause that loss? We destroy critically important habitat and we overhunt large animals.

Beware Rodents Bearing Suitcases… and Diseases

Loss of habitat and human predation cause the loss of large animal species. Think elephants, zebras, lions, tigers, rhinos and giraffes. Once those major animal players disappear from a land-based ecosystem, the rodents gleefully move in and become king of the manor. There’s no animal bigger and badder to keep them in check anymore.

Rodents carry with them all manner of disease and pestilence. All of a sudden those diseases take hold, sweeping the world and cutting down all creatures in their path.

This isn’t guesswork. Scientists have watched it happen. According to the study team’s press release:

[P]revious experiments conducted in Kenya have isolated patches of land from megafauna such as zebras, giraffes and elephants, and observed how an ecosystem reacts to the removal of its largest species. Rather quickly, these areas become overwhelmed with rodents. Grass and shrubs increase and the rate of soil compaction decreases. Seeds and shelter become more easily available, and the risk of predation drops.

Consequently, the number of rodents doubles – and so does the abundance of the disease-carrying ectoparasites that they harbor.

“Where human density is high, you get high rates of defaunation, high incidence of rodents, and thus high levels of pathogens, which increases the risks of disease transmission,” said lead study author Rodolfo Dirzo, Stanford University professor of biology. “Who would have thought that just defaunation would have all these dramatic consequences? But it can be a vicious circle.”

Between 16 and 33 percent of all vertebrate species are considered globally threatened or endangered, according to the study. It’s not just the big animals we need to worry about, however.

Invertebrates – particularly insects like spiders, butterflies, worms and beetles – are in decline as well. The study notes that while the number of humans has doubled in the last 35 years, the number of invertebrates has fallen by 45 percent. This, too, happens because of “habitat loss and global climate disruption,” said the Stanford press release.

Nearly 100 percent of Orthoptera species such as grasshoppers, crickets and katydids are in decline. Butterflies and other Lepidoptera face a 35 percent drop. These are only two examples in a world filled with similar unfortunate statistics.

We need invertebrates if we are to survive. Insects, for example, pollinate three quarters of the world’s crops. Without them, processes like nutrient recycling and decomposition become problematic. Remember the problems we’re having because of the decline in bees? Expand those issues to include all invertebrates and the ramifications become deeply worrisome.

“We were shocked to find similar losses in invertebrates as with larger animals, as we previously thought invertebrates to be more resilient,” Ben Collen of the U.K.’s University College London, told USA Today.

It‘s Not Too Late, But We‘re Perilously Close

“We tend to think about extinction as loss of a species from the face of Earth, and that’s very important, but there’s a loss of critical ecosystem functioning in which animals play a central role that we need to pay attention to as well,” Prof. Dirzo said.

Estimates say we still have perhaps a century or so to adjust how we do things and reverse this mass extinction trend. The types of change we need to embrace require commitment and resolve.

Reversing the early stages of our plant’s sixth mass extinction event will require a wholesale course correction in how we’re dealing with climate change, say some experts. We will need to employ what Scientific American calls “aggressive conservation” to preserve species that are on the edge of extinction.

Can we do it? Can we get it together in time, or is the Age of Humans about to be consigned to history?

Photo credit: Thinkstock

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219 comments

Craig b.,
I agree with your first statement, but not necessarily your second. While overhunting led to precariously large declines in several species, recent awareness has caused some to rebound. I mentioned several of the recent successes previously. Will this extend to other species? I do not know. However, recent action is encouraging. What is not, is continued deforestation, particularly in the tropics. Destroying these ecosystems, cab have far-reaching effects. Habitat destruction has been our greatest detriment to nature, and steps to reverse such have been sparce and slow.

Is it too late to reverse course? NO.
Will we reverse course? NO...
Our Grand Children are going to Hate US for the Death we are leaving for Them.
GOtP Greed, Insanity, Bigotry and Ignorance Win!!!
I get the feeling this is insanity repeating itself...

There are 3 things that differentiate this mass extinction from the previous 5. One is the fact that this is the only one caused by the greed, stupidity and outright recklessness another species - human beings as is the case.

But the other 2 are equally important:

2. Mass extinctions generally occur over geological time ... tens or hundreds of thousands of years. This one has occurred irecord time ... basically the bginning of the industrial revolution.

3. Every other Mass Extinction started at the top of the food chain and worked it's way down, thus dwindling out before things got too, too bad ... bad enough for sure, but: THIS ONE started at the bottom of the food chain (plants and insects primarily even though we hear mostly about tigers, apes, etc.) and is working it's way up.

Take a moment and think about the ramifications of that.

The be afraid, Very afraid.

And consider the possibility that we may need to do much, much more than sign petitions (though we should still do that too).

You have now unwittingly joined an eclectic educated and informed group of about 2 dozen of us who have been just as amused as you are by the absence of this individuals intellect. He has been roundly called, out, challenged,debated and successfully debunked time and time again for his pompous, inane, unsupported claims here on Care2.

His most recent comment to you, naming me, is an attempt to get back at me for my part in showing him embarrassingly how wrong he has been over and over again.

Its great to make your acquaintance. Glad to have you on board calling a spade a spade.

I have known about this for a while but it is sad. We have to limit population of people on this earth. Our population is not sustainable at 6 or 7 billion. The animals and the green spaces are suffering and when they go, we eventually will.